FF-P-386 — Pin, Cotter (Split)
FF-P-386 covers split cotter pins — simple, low-cost locking devices inserted through a cross-drilled hole in a bolt, nut, or shaft and bent open to prevent the assembly from backing off under vibration. Revision D dates to December 16, 1971 and remains active.
At a Glance
Overview
FF-P-386 covers split cotter pins — semi-circular cross-section wire formed into two legs joined at a rounded or looped head, inserted through a cross-drilled hole in a bolt, castle nut, clevis pin, or shaft. Once installed, the two legs are bent apart (typically one leg bent over the end and one along the side) to mechanically prevent the pin from backing out, which in turn locks the fastener assembly against loosening from vibration or rotation.
Cotter pins are one of the simplest and most reliable mechanical locking devices in the fastener toolkit — unlike self-locking or prevailing-torque devices, they provide a purely mechanical block against rotation rather than relying on friction, making them a favored solution for high-vibration or safety-critical joints such as landing gear, castle nut assemblies, and clevis connections.
- Cotter pins are inherently single-use: once bent open for installation, they should not be straightened and reused, as repeated bending fatigues and weakens the material.
- Common material/finish combinations include cadmium-plated carbon steel (per QQ-P-416 Type 2, Class 3) for general use, and corrosion resistant steel or brass for wet, marine, or non-magnetic applications.
Material Options
FF-P-386 — Frequently Asked Questions
Can a cotter pin be reused after removal?
No — once bent open for installation, a cotter pin should not be straightened and reinstalled. The bending process fatigues and weakens the material, so a new pin should be used at each assembly.
What's the difference between a cotter pin and a self-locking nut?
A cotter pin provides a purely mechanical block against rotation by physically obstructing the fastener, while a self-locking nut relies on friction (from a prevailing-torque feature or non-metallic insert) — cotter pins are often preferred for safety-critical joints because their locking action doesn't degrade with vibration the way friction-based locking can.
Need FF-P-386 Cotter Pins to Print?
Ananka Fasteners manufactures FF-P-386 split cotter pins with full material traceability and Mill Test Certification.
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